1. Field of the Invention
The present invention relates generally to wireless communication. More particularly, the present invention relates to circulation transmissions for Multiple-Input-Multiple-Output (MIMO) systems containing multiple transmitter and receiver antennas.
2. Background Art
An advantage of such MIMO systems is that by using multiple transmitter and receiver antennas to transmit and receive multiple data streams at the same time MIMO systems boost the data throughput multiple times. System performance in a MIMO system can be optimized by transmitting the data streams with a Gaussian distribution. That is, the transmitted data streams should be independent and have zero correlation. One way to achieve such independence is to try to exploit all available diversities, i.e., diversities in frequency, time and space, when transmitting the data streams. Consequently, a MIMO system realizes its best performance by exploiting the maximal randomness (or minimal correlation) of the transmitted data streams in frequency, time and space.
Due to device size limitations, antennas must be placed close to one another. Unfortunately, such proximity causes the transmitted and received data streams to be highly correlated, which, in turn, degrades system performance. Therefore, it is desirable to minimize the correlation of transmitted data streams, and thereby improve the performance of a MIMO system.